Human lung cancer cell lines exhibit resistance to retinoic acid treatment

Retinoic acid (RA) and nuclear retinoic acid receptors (RARs) have been implicated in a variety of human malignancies including lung cancer, and RA has been proposed as a chemopreventive agent for bronchogenic carcinoma. Normal human tracheobronchial epithelial cells show dramatic induction of RAR- mRNA and significant growth inhibition after RA treatment. In contrast, 1 7 of 22 small cell lung cancer (SCLC) and 9 of 15 non-SCLC lines treated with 1 M RA showed no significant growth inhibition. Of interest, 5 SCIC lines with high levels of myc gene family expression related to c-, N-, or L-myc gene amplification exhibited growth inhibition (28-87%), whereas 2 non-SCLC lines adually showed growth stimulation after treatment with 1 M RA. The lines varied greatly in their constitutiv